The present invention relates generally to a method and apparatus for protecting a pier. More particularly, the invention relates to a self-supporting docking fender which hydraulically dissipates the energy of forces applied thereto and which is positively restrained both laterally and axially.
The sudden increase in the degree of industrialization and affluence through much of the world has resulted in burgeoning international trade. Great quantities of goods are being routinely transported over enormous distances. A portion of these goods, particularly perishable materials, are transported by air. A considerably larger proportion of the goods are transported by land. However, the major and most economical mode of transporting materials in world trade is by water. Thus, great quantities of both raw and finished materials are transported by ship and most commonly by large ocean going vessels.
As ocean going trade has become more voluminous, the fixed unit construction and operating costs of the cargo vessels have produced a trend toward large ships. Accordingly, facilities capable of handling smaller vessels suddenly have become inadequate for handling the hugh vessels seeking to come to port. For instance, many natural harbors which serve as distribution centers to inland industrial areas are simply too shallow to accommodate the deep draft of many modern heavily loaded ships. This is particularly true of those vessels referred to as supertankers which carry petroleum and liquified natural gas in international trade. In the case of these supertankers, the problem of insufficiently deep natural harbors is circumvented by constructing large offshore terminals where the water is sufficiently deep to accommodate the ship. Oil or liquified natural gas can be pumped to or from the terminal and loaded or unloaded aboard the ship.
When an offshore terminal is used, the super tankers are commonly moored during loading and unloading to mooring dolphins. These mooring dolphins consist essentially of large, slender towers extending from the floor of the body of water upwardly to protrude a desired distance above the water. In addition to being moored to the mooring dolphin, the tanker is normally berthed along side a number of breasting dolphins or similar pier structures. It should be apparent that during berthing a ship the size of a super tanker can impact and severely damage the breasting dolphins or pier. Likewise, once berthed, the motion of waves can cause the ship to impact or at least cyclically bear against the breasting dolphins or pier in a manner likely to cause considerable damage. In order to minimize damage which might occur incident to the exertion of dynamic forces due to impacts or wave motion as described above, it may be advantageous to provide docking fenders to dissipate the energy of the cyclic forces and thereby protect the breasting dolphins or pier and the hull of a ship.
It will be appreciated that similar problems occur in connection with more conventional facilities provided within a natural harbor. In this case, a ship is commonly berthed adjacent a wharf or other pier structure extending from the land out into the harbor. Just as in the case of offshore terminals, a ship may impact the wharf or pier during berthing. The problem of wave action, however, may be somewhat less severe since the harbor may be substantially more sheltered from the open sea and therefore less likely to receive the effects of significant wave action. Nonetheless, there exists an additional source of damage due to rising and falling tides. It should be readily appreciated that in the time required to load and unload a ship, the tides may raise and lower the ship several times and cause undesirable contact between the ship and the pier resulting in damage to the pier. As in the case of offshore terminals, damage of the sort which may be caused by dynamic forces exerted by a ship may be significantly reduced by the use of docking fenders to protect the wharf or pier.
Docking fenders of various types have been employed in attempts to alleviate problems of the type mentioned in the preceding. For various reasons these docking fenders have not been entirely successful and have presented a number of problems. For instance, a considerable number of the docking fenders presently in use employ simple, elastomeric bumpers or springs or other resilient elements to dissipate the energy of forces exerted against the fenders. While fenders of this type may be effective under some circumstances, they may not dissipate sufficient amounts of energy to satisfactorily accommodate very large vessels such as the super tankers mentioned in the preceding.
To increase the quantum of energy which can be dissipated, some docking fenders of the prior art may employ hydraulic cushions or dampers between the pier and a bumper intended to be contacted by the ship. While these devices may be more effective in dissipating energy, many such arrangements fail to provide a docking fender in which the bumper initially contacted by the ship is entirely free to translate and compress the hydraulic cushions or dampers. For instance, a bumper which is contacted by the hull of a ship may in some cases be pivoted along one edge and hydraulically cushioned by dampers disposed along the opposed edge. The energy dissipating qualities may thus be limited by the restricted movement of the bumper.
In other cases, while the bumper may be entirely free to move in response to forces exerted by the ship, the bumper may be supported and cushioned only by splayed, hydraulic cushions which interconnect the bumper and the pier. As a result, each cushion experiences less compression as the bumper is displaced toward the pier than if the cushions were orthogonally oriented between the bumper and the pier. Furthermore, in an arrangement in which the bumper is supported and cushioned by splayed cushions, the fender may be more vulnerable to the effects of glancing impacts or forces applied parallel to the surface of the bumper. Such impacts or forces may tend to displace the bumper laterally and thereby render the cushioning effect less effective. Additionally, lateral displacement of the bumper relative to the pier may cause damage to one or more of the cushioning units or to the connections between the cushions and the bumper or pier. Also, without a secondary supporting structure the splayed cushions may not provide sufficient vertical support to prevent vertical sagging of the bumper. Thus, it can be appreciated from the preceding that many docking fenders of the prior art which employ hydraulic cushioning units to dissipate the energy of forces applied to the fender may suffer the disadvantage that the bumper which receives the forces is not adequately restrained laterally against the effects of gravity and/or forces applied parallel to the surface of the bumper.
Somewhat related to the problem of restraining lateral displacement of the bumper relative to the pier is the problem of limiting displacement of the bumper axially away from the pier. Many fenders of the prior employing hydraulic cushions may make no provision for any positive limitation to the degree of spatial separation between the bumper and the pier. This lack of positive restraint may permit the cushions to be damaged should they be forced into a hyperextended or overtraveled condition. Similarly, many docking fenders of the prior art which employ hydraulic cushions to dissipate the energy of forces applied to the fender may provide no effective limitation to the degree of compression of the hydraulic cushions. If the fender is subjected to impacts which fully compress the cushions, then further impacts can not be cushioned. In other words, once the cushions are fully compressed, the fender becomes essentially a rigid structure incapable of absorbing and dissipating the energy of further applied forces. In this fully compressed, essentially rigid condition, the fender itself is as vulnerable to damage as would be an unprotected dock or pier.
In many offshore terminals and conventional harbor facilities alike, the space available for a docking fender may be somewhat limited. Thus, it can be appreciated that docking fenders which require large supportive or restraining structures may not be entirely suitable. In particular, if the elements which cushion, restrain, or otherwise connect the bumper and pier, extend from between the bumper and pier, undue amounts of space may be occupied. Even if space is not limited, elements extending from between the bumper and pier may be vulnerable to damage from impacts which may be received from the ship or equipment associated with the pier.
The problems enumerated in the preceding are among many which tend to reduce the effectiveness of previously known docking fenders. Other noteworthy problems may also exist, however, those presented in the discussion above should be sufficient to demonstrate that the docking fenders appearing in the art have not been altogether satisfactory. A docking fender according to the present invention is intended to at least obviate or minimize problems such as those mentioned above.
A docking fender according to the present invention receives dynamic forces exerted by the hull of a vessel through a generally planar, vertically oriented bumper which is connected in spaced relation to a side of a pier which is similarly generally planar and vertically oriented. As the dynamic forces are received, the bumper is displaced axially towards the pier in response to the components of the dynamic forces acting normally against the bumper. The energy of these normal components is dissipated by axially telescoping, hydraulic cushioning units orthogonally disposed between and connecting the bumper and the pier. The cushioning units dissipate the energy of these normal components by developing internal reactive forces which tend to resist axial compression of the cushions. Once the energy of the normal components of the dynamic forces is dissipated, the hydraulic cushions automatically restore themselves and return the bumper to a fully extended condition.
Lateral displacement of the bumper relative to the pier in response to components of the dynamic forces exerted parallel to the bumper is rigidly restrained at all times. This restraint is exerted by vertically inclined counters which exert generally lateral tensile forces between the bumper and the pier. The counters diagonally connect the bumper and the pier at points adjacent the corners within the perimeter of the bumper.
Hyperextension or overtravel of the cushions due to excessive axial displacement of the bumper away from the pier is prevented by means of axial counters which connect the bumper and the pier to positively restrain the bumper. This axial restraint prevents displacement of the bumper axially away from the pier beyond a prescribed distance at which the cushioning units are fully extended. At least one axial counter is disposed adjacent each of the cushioning units and all of the counters are disposed within the perimeter of the bumper.
Hypercompression or compressive overtravel of the cushioning units is prevented by means of a plurality of abutting members rigidly cantilevered from the pier. The free ends of the abutting members are coplanar and resilient and abut the inside surface of the bumper to prevent undue displacement of the bumper axially toward the pier. The positive limitation of displacement of the bumper axially toward the pier precludes excessive compression of the cushioning units.
In presenting the invention reference will now be made to a preferred embodiment. This preferred embodiment is by way of example and not by way of restriction or limitation with respect to the present invention and the manner in which it may be practiced.